Hmm, you are talking about 'Advanced iText' only and ignoring the 'Simple iText' functionality. iText allows you to work with a com.lowagie.text.Document-object and add high-level objects such as Paragraph, Phrase, Chunk,...
In that case, you needn't know anything about the coordinate system. You just keep on adding objects and if the end of a page is reached, a new page is automatically started (as one would expect).